Field of the Invention
The present invention relates generally to a gas turbine engine, and more specifically to a radial acting seal located in the turbine section between the stator vane and the rotor.
Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In an industrial gas turbine engine, a turbine includes three or four rows or stages of stator vanes and rotor blades that guide and react with a hot gas flow to convert the energy from the gas flow into mechanical work by driving the turbine rotor shaft from which the rotor blades are connected to. As the hot gas flow passes through the stages, the pressure decreases as energy is extracted by the rotor blades. The rotor blades are positioned between adjacent stages of stator vanes. A seal is required between the rotor and the stator to prevent hot gas flow from leaking into the rim cavity or other areas outside of the main flow path in which the elevated temperature of the gas flow can affect other parts of the turbine such as the rotor disks. Also, the seals between the stages of vanes and blades prevent leakage of the higher pressure gas flow into a lower pressure gas flow at a downstream stage of the turbine.
Turbine stages typically use labyrinth seals or brush seals to limit leakage flow. Labyrinth seals provide a good seal at high rotational speeds and can allow for slight amounts of rub against a honey comb surface. Brush seals make good seals for low rotational speeds, but wear relatively fast at very high speeds. One major problem with an industrial gas turbine engine and these interstage seals in the turbine is when transients occur. In a transient, the engine operate from a cold condition to a steady state operating condition, or goes from one condition to another condition in which the rotor shaft and the casing changes temperatures that cause relative radial displacement between the shaft and casing. This relative radial displacement will cause significant gap clearances in the interstage seals to open or close such that the leakage flow is significantly increased or a rubbing occurs that will damage or wear out the seal prematurely.
One example of this transient is when an engine is shut down from a steady state operation to a stopped condition. The casing will cool quicker than the rotor shaft, so the casing will close down on the rotor shaft. In another transient condition, the stopped engine will be restarted. The casing will heat up quicker than the rotor shaft so that the casing will thermally grow in a radial direction faster than the rotor shaft will. Thus, the clearance gaps during transients change such that large gaps are produced or rubbing is produced.
U.S. Pat. No. 8,133,014 issued to Ebert et al. on Mar. 13, 2012 and entitled TRIPLE ACTING RADIAL SEAL (the entire disclosure being incorporated herein by reference) discloses a triple acting radial seal used as an interstage seal assembly in a gas turbine engine, where the seal assembly includes an interstage seal support extending from a stationary inner shroud of a vane ring, the interstage seal support includes a larger annular radial inward facing groove in which an outer annular floating seal assembly is secured for radial displacement, and the outer annular floating seal assembly includes a smaller annular radial inward facing groove in which an inner annular floating seal assembly is secured also for radial displacement. A compliant seal is secured to the inner annular floating seal assembly. The outer annular floating seal assembly encapsulates the inner annular floating seal assembly which is made from a very low alpha material in order to reduce thermal stress.